The present invention relates to a storage device and a write access processing method for a storage device.
This storage device provides a storage area based on a RAID (Redundant Arrays of Inexpensive Disks) system, wherein disk drives, such as hard disk drives, or the like, are arranged in an array configuration. A host computer (hereinafter, called “host”) accesses the logical storage area provided by the storage device and reads or writes data.
The storage device stores write data received from the host, on the disk drives, via a cache memory. Furthermore, for example, if data requested by the host is not stored in the cache memory, then the storage device reads out the data requested by the host, from a disk drive, stores that data in the cache memory, and then supplies the data to the host via the cache memory.
In this way, write data requested for writing by the host is held in the cache memory, and then written to a prescribed disk drive. The method for writing data from the cache memory to a disk drive can be divided broadly into two types of method.
One method is a so-called “write-through” method, for example, wherein the writing of write data to the cache memory and the writing of write data to the disk drive is carried out in a substantially simultaneous fashion. The other method is a so-called “copy back” method or “after-write” method, for example, wherein the write data is stored in the cache memory only, and at a prescribed timing thereafter, the write data in the cache memory is written to a disk drive (see Japanese Patent Laid-open No. (Hei)6-309232.)
In the write-through method, the completion of the write operation is reported to the host when the write data has been written to the disk drive. In the after-write method, the completion of the write operation is reported to the host when the write data has been stored in the cache memory. Therefore, the after-write method allows the response time to be compressed to a greater extent than the write-through method.